Recently in the production of semiconductor devices and liquid crystal display devices, pattern size reduction has been developed rapidly with advances in lithography techniques. Accordingly, there is a demand for high resolution such as a pattern having a width of 50 nm or less.
For pattern size reduction, in general, short wavelength exposure sources has been increasingly used. Besides the currently used KrF excimer laser, lithography techniques using exposure lights such as ArF, F2, EUV, x-rays, electron beams and other charged particle beams have been proposed.
Especially, pattern forming techniques using exposure to electron beams and EUV are positioned as the second-generation or the third-generation lithography techniques, and there is a demand for the development of a negative resist for forming the gate layer of a semiconductor integrated circuit or processing a mask pattern to be formed on a glass substrate, which meets all the requests for high sensitivity, high resolution and low line edge roughness (LER).
As the resist material which meets such requests, a chemically amplified photosensitive composition is used, which utilizes the catalytic reaction of acid for the purpose of increasing sensitivity. A negative, chemically amplified photosensitive composition generally comprises an alkali-soluble resin, which will be the resist substrate, an acid generator component which produces acid by exposure to light, a crosslinking agent, a basic compound, etc. When such a photosensitive composition is exposed to light, a crosslinking bond is formed between the resin and crosslinking agent by the action of acid produced from the acid generator component by the exposure; therefore, the photosensitive composition is changed from an alkali-soluble composition to an alkali-insoluble composition. Also, pattern exposure is possible with a smaller exposure amount since the acid produced by the crosslinking reaction catalytically repeats reaction. On the other hand, in the chemically amplified photosensitive composition, there is a contradictory relationship between sensitivity, resolution and LER, and an issue for the composition is how to balance them.
A resist material comprising a polymer having a weight average molecular weight of about 5,000 or more, has been used for the alkali-soluble resin to be the resist substrate in semiconductor lithography.
However, such a polymer material has a large molecular weight and a wide molecular weight distribution, so that there is a limit to decreasing resolution or LER.
Accordingly, as the alkali-soluble resin to be the resist substrate, low-molecular-weight materials have been under development. The low-molecular-weight materials are expected to have better resolution than polymer materials and also to decrease LER. Examples of negative resists comprising such low-molecular-weight materials as the resist substrate include a resist comprising calix resorcinarene and a derivative thereof (Patent Literature 1 and Non-Patent Literature 1), a resist comprising a low-molecular-weight polyphenol compound derivative (Non-Patent Literature 2) and a resist comprising a cyclic polyphenol compound derivative (Patent Literature 2).
Also recently, a molecular resist based on cationic polymerization was reported in the field of negative, chemically amplified resist compositions (Non-Patent Literature 3). The molecular resist based on cationic polymerization utilizes the crosslinking ability of epoxy groups; therefore, it needs no crosslinking agent that has been used therefor. However, since the molecular resist of Non-Patent Literature 3 comprises no phenolic hydroxyl group, it cannot be developed in alkali developing solutions production. It is described in Non-Patent Literature 3 that the molecular resist based on cationic polymerization offers high sensitivity, high resolution and low LER; however, as shown in reference examples described later, it was found that the resist has a problem with dimensional stability of pattern and such a problem that dewetting occurs in the step of forming a coating film for forming a pattern (in a post-applied bake treatment), so that it is not possible to form a uniform resist film and thus to obtain a fine pattern with low LER.
A negative resist composition is disclosed in Patent Literature 3, which comprises a polymer with alkali developing property and crosslinking ability. However, in the case of using the polymer with alkali developing property and crosslinking ability, swelling is likely to occur upon development and no fine pattern with low LER can be formed due to pattern collapse or waved pattern caused by the swelling.
Also, imprinting has been attracting attention as a new lithography technique.
Especially, there is a demand for development of a resist with a resolution of 20 nm or less, which is used as a resist for producing an imprint mold that is used as an original plate in lithography, or for producing a gate layer of a semiconductor circuit by electron beam direct writing.
As a resist material that meets the demand, a positive resist composition mainly comprising an α-methylstyrene-α-chloroacrylic acid methyl ester copolymer, is commonly used.
Moreover, a calixarene resist (Non-Patent Literature 4) and a hydrogen silsesquioxane (HSQ) resist (Non-Patent Literature 5) have been proposed as negative resists with a resolution of about 10 nm.
As described above, calixarene is useful as a super-resolution resist for research and development or trial production because it functions as a negative resist and provides a resolution of about 10 nm. However, organic solvents such as xylene are used for development of this resist. Since these developing solutions are used in a large amount in the pattern formation process and volatile, it is difficult to collect them absolutely and thus to use them on mass production lines such as semiconductor integrated circuit production.
Meanwhile, the HSQ resist has characteristics such as a resolution of about 10 nm and high etching resistance, and alkali developing solutions can be used for development of the resist. However, this resist material has a problem of poor line width stability during electron beam writing (change in sensitivity during writing). “Line width stability during electron beam writing” means that a change in line width in vacuum during the time between electron beam writing and development. Since time lapses after writing and before development differs between the beginning and end of the writing of a surface of a substrate, there is a problem of change in pattern line width even on the same surface of the substrate (Non-Patent Literature 6). Since HSQ is an inorganic compound, there is also such a problem that it is difficult to remove a resist residue left between patterns by ozone or plasma asking in a gas phase.